President. This is the text of this article from the 1911 Encyclopedia Britannica at a third party site. It only briefly touches on the concept of the American Presidency but I thought the overall article on the idea of a president and how it has evolved over time was interesting.
From the site:
PRESIDENT (Fr. president, from Lat. praesidens, postAugustan Lat. for praeses, director, ruler, from praesidere, to sit in front of, preside), a style or title of various connotation, but always conveying the sense of one who presides. In classical Latin the title praeses, or president, was given to all governors of provinces, but was confined in the time of Diocletian to the procurators who, as lieutenants of the emperor, governed the smaller provinces. In this sense it survived in the middle ages. Du Cange gives instances from the capitularies of Charlemagne of the style ~raeses provinciae as applied to the count; and later examples of praeses, or praesidens, as used of royal seneschals and other officials having jurisdiction under the Crown.
In England the word survived late in this sense of royal lieutenant. Thus, John Cowell, in his Interpreter of Words (1607) defines President as used in Common Law for the Kings lieutenant in any province or function; as President of Wales, of York, of Berwick. President of the Kings Council. In some of the British North American colonies (New Hampshire, Pennsylvania, South Carolina) there was a president of the council, usually elected by the council; and when Pennsylvania and New Hampshire became states, one member of the Executive Council was called president. The chief (and single) executive head in Delaware, South Carolina and New Hampshire (1784-1792) was called president.
During the revolutionary struggle in America from 1774 onwards, the presiding officer of the Continental Congress was styled President and when the present constitution of the United States was framed in 1787 (in effect 1789) the title of President was transferred to the head of the Federal government. President thus became the accepted style for the elected chief of a modern republic, the example of the United States being followed by the South American republics; by France in 1849, and by Switzerland.